Propane dewaxing



Nov. 2, 1937. P. c. KEITH, JR

PROPANE DEWAXING Filed April 30, 1934 Nh mvk/ w i n@ t 7 QW nm. mvnw a Y. Em u Rx u @@.m QW Nm. mum. m6. D0 QQ@ NN mm. m y n SS Y m m A k Mw x .E @w MN www ov, @QQ Om; ww mmf @w r mw @mY Se. E )w/ SRQNQ k mm www@ QRGQOKQ @N mm QQ u www Patented Nov. 2, 1937 acme PATENT PROPANE DEWAXING Percy C. Keith, Jr., Peapack, N. J., assigner to Standard Oil Company,

ration of Indiana Application April 30,

1 Claim.

This invention relates to an improved method and means for producing low pour point lubricants from wax-bearing oil stocks and it pertains more particularly to a process and apparatus for 5 dewaxing oils with liqueed normally gaseous diluents.

It has been found that liqueed normally gaseous diluents such as propane oier many important advantages in the dewaxing of mineral oils. They permit or cause the crystallization of wax in readily lilterable or settleable form even though the wax is of such nature that it could not be commercially ltered or settled from ordinary naphtha diluents. They permit the use of rapid chilling in obtaining lterable wax even though the refrigeration be applied indirectly instead of by direct vaporization oi diluent from the diluted oil-wax mixture. They make it possible to obtain high yields of low pour point oils and relatively dry wax cakes. They facilitate extremely rapid filtration or settling. The removal of these diluents from dewaxed oil actually supplies refrigeration to the system and requires a minimum amount of heat and stripping steam. The object of my invention is to utilize all of these advantages and to provide a commercial dewaxing system which will require a minimum amount of equipment, power and steam, which will be exible and therefore applicable to all types of oils, and which will give maximum yields of low pour point lubricating oils.

A further object is to provide a method and means for operating a propane dewaxing plant in a continuous manner, preferably in both the chilling and the wax-separation stages. A further object is to provide an improved system. for operating lilters and for furnishing and utilizing blow-back gases therein.

A further object is to divide the system into high pressure and moderate pressure groups of elements, to stabilize the pressure, particularly in the latter group of elements, by means of a large pressure gas tank and to utilize the gas from said tank both for facilitating filtration and cake drying and for furnishing refrigeration.

A further object is to provide a two-component diluent system having a high pressure storage tank containing chiefly the heavier component in the liquid phase and a moderate pressure storage tank containing chiefly the lighter diluent component in the gaseous phase A further object is to regulate temperatures and pressures in various parts of the system to proportion the amounts of light and heavy components of the diluent in the respective parts of the system.

Chicago, Ill., a corpo- 1934, serial No. 723,043

A further object isto provide a high pressure, intermediate pressure, and low pressure diluent storage system which is so interconnected that the temperature and composition of the diluent in the low pressure storage tank are both controlled by regulating the injection and vaporization of varying amounts oi diluent from the high pressure and intermediate pressure systems respectively.

A further object is to provide an improved means for chilling waxy oil in a normally gaseous diluent and supplying additional diluent to the oil after chilling and in such a manner that it will not appreciably raise the pour point of the finished oil, but will retain all the advantages of an extremely large diluent to oil ratio. Other objects will be apparent as the detailed description of my invention proceeds.

My invention will be described rst as applied to a single component diluent system such as propane and then as applied to a system employing a two-component diluent such as a mixture of propane and ethane. In the first case, the waxy oil is dissolved in an equal part of propane, the wax is solidilied in countercurrent exchangers and is passed to a chilled storage tank irom which it is pumped into continuous or batch lters. The oil being passed to the lilters is diluted withA substantially pure propane which is preferably slightly colder than the chilled wax slurry and the filtration step at such a low temperature that the diluent propane will not dissolve an appreciable amount of wax. The lilter cake may be washed with propane and it is nally blown with propane gas from an intermediate pressure gas storage system. The cold propane diluent and wash propane is prepared by vaporizing propane from the high pressure propane storage tank and condensed blow gases in varying proportions. The dewaxed oil is passed through the exchangers to furnish refrigeration. The wax cake is passed to a surge chamber which is vented to the intermediate pressure storage tank. Both wax and oil are nally passed through their respective high pressure and low pressure diluent removal systems. A feature of this system is the venting of low pressure diluent reboilers, wax surge tank, etc., to the intermediate pressure gas storage tank which is also 4connected through a valved line to the vapor space of the high pressure storage tank and which acts as a reservoir for gases compressed from the chilled wax slurry storage and the cold propane storage tank. It will thus be seen that compressor requirements are low, an intermediate safe pressure is insured 55 throughout the larger part of the system, and an eicient and effective blow-back means is provided for the ltering and cake drying steps.

When I employ a propane-ethane mixture the advantages of my system are even more pronounced and my compressor requirements and costs are still further reduced. In this case the Y high pressure propane storage tank will contain chiefly propane, my intermediate pressure gas storage tank will contain chiey ethane, and the relative amounts of ethane and propane in the cold propane storage tank may be varied at will by proportioning the amount of diluent introduced from the high pressure and the intermediate pressure tanks respectively. In this system the blow-back gas is chiefly ethane which will not condense or dissolve appreciable amounts of wax in the lter. The use of ethane may indeed obviate pressor between either the wax slurry storage tank or the cold propane storage -tank-Zand the intermediate pressure will be more clearly understood from the following detailed description.

In the accompanying drawing which forms av part of this specification, I have shown a iiowsheet or a plan of my improved system with the various elements diagrammatically indicated.

The term propane as used hereinin expressly defined to include equivalent normally gaseous diluents, particularly hydrocarbons of from two to four or five carbon atoms and mixtures thereof. In other words, this expression is intended to include ethane, propane, isobutane, normal butane, propylene, butylene, etc. and mixtures thereof, even those mixtures which contain small amounts of pentane, hexane, etc. Other normally gaseous substances such as sulfur dioxide, dichlor diflor methane, other halogenated substitution products of methane and ethane, normally gaseous ethers, gaseous amines,

`ammonia carbon dioxide, etc. may be used in place of propane or in admixture therewith. When the expressions propane and ethane are employed, it is to be understood that these terms refer to diluents of different boiling points and that any of the above diluents may be employed so long as one component of the normally gaseous diluent has a higher boiling point than the other. This invention relates primarily to the technique of dewaxing with normally gaseous diluents and mixtures thereof and it is not dependent upon the use of any specific diluent or diluent mixture.

The invention may be employed for the dewaxing of any wax-bearing oil, but it is particularly useful in the dewaxing of petroleum distillates or residues from which asphalt has been separated. The invention is also useful on stocks containing suiiicient asphalt or pour point depressor to act as a lter aid o-r settling aid-and to carry down the wax in readily separable form. The invention will be described asY applied to overhead S. A. E. Mid-Continent lubricating oil stock which has had a preliminary acid treatment, but it should be understood-that the invention is applicable to any type of wax-bearing oil either before or after solvent extraction, clay or esses.

chemical treatments, other refining proc- 'Ihe waxy oil stock is introduced into the sys-Y tem through pipe IS preferably at a temperature at which it is fluid and it is admixed with about one part by volume of propane from line I I. The

mixing step may `take place directly in the transthe necessity of any `comgas tank. The invention fer pipes or in any suitable mixing apparatus and if necessary the mixture is passed through an exchanger I2 wherein it is heated with steam to bring about complete solution of the waxy oil stock in the propane. In this case the temperature is about 135 F. but it may vary for dinerent stocks from about to 150 F. This solution may then be passed through a preliminary cooler I3 in the form of a cold water exchanger, Scrapers being employed if necessary to prevent adherence of wax to the walls of the exchanger. The solution or slurry is then passed through a series of counter-current exchangers I 4, having cooling jackets I5 through which cold, dewaxed oil and filtrate are passed by means of pipe I5. The flow of waxy oil stock in these exchangers is opposed to the flow of cold ltrate, so that the cooling is gradual and shock chilling is prevented. I have found that when propane is used as a diluent, lterable wax crystals can be obtainedin this manner even when relatively high chilling rates are employed. I may use. scraped surface exchangers of the conventional type, commonly known as Carbondale Chillers,- or I may use any equivalent devices.

The diluted oil-wax slurry leaving therexchangers may be at a temperature of about -40 F. or at least at a sufficiently low temperature so; that no deleterious shock chilling will take place when the mixture passes through valve Il in pipe I8 to chilled wax slurry storage tank. I9. Additional cold diluent may be introduced into this storage tank through line 2G and cooling is effected by vapcrizing propane from the top of the tank through pipe 2 I, compressor 22 and pipe fr 23 to intermediate pressure gas storage tank 24. When a mixture of propane and ethane is used as a diluent, compressor 22 may be by-passed by line 25.

I retain slurry in tank of time because I find long standing impairs lter rates. In one instance a slurry which stood for 7 hours was diiicult to iilter and gave Vpoor. lter rates-long standing may cause a crystal rearrangement which is very deleterious to both filter rates and yields. Slurry from the base of tank I9 is passed through pipe 26, admixed with additional cold propane from pipe 2l and mixedv and forced by pump 28 to pipe 29. As will be hereinafter explained, this propane is slightly colder than the propane-oil-wax slurry and its presence in contact with the wax causes no substantial wax solution or deleterious crystal formation. I prefer to add about one to four volurnes' of propane through line 21 to each volume of oil-wax mixture.

Filter 30 is preferably of the continuous rotary pressure type enclosed in a gas-tight, insulated pressure casing. Dewaxed oil is continuously withdrawn from the filter through pipe 3I toy surge tank 32. Wax cake is continuously withdrawn from the lter through line 33 by means of a screw conveyor 34 to surge tank 35. Precooled wash propane is introduced through pipe 36 and the washed oil which is removed by this propane is returned through pipe 3l to cold storage tank I9, is mixed with the dewaxed oil, or `is trans- I9 for a minimum period A with the filtrate, is separated from liquids in chamber 32 and is then passed through pipe 40, compressed by compressor 4|, and introduced by pipe 42 to cooler 43 in which it is liqueied.` It is then passed through pressure release valve`44 and allowed to Vaporize and expand in cold diluent storage tank 45 thereby cooling the diluent stored therein. When propane is employed as a single solvent I prefer to maintain tank 45 at about zero pounds gauge, but when a mixture of propane and ethane is employed I prefer to operate at a higher pressure, preferably to 50 pounds gauge. Vapors are remove-d from the top of tank through pipe 46 which leads `to pipe 2l, compressor 22, pipe 23 and intermediate gas storage tank 24.

InA operating my filtersystem I find that large volumes of blow gas are necessary and I therefore employ a relatively large intermediate pressure gas storage tank which is preferably maintained at a pressure of about 0 to 50 pounds gauge. This tank may be cylindrical, spherical or spheroidal or it may be in the form of a gas holder. Gas from this tank may be introduced through pipe 39 to maintain pressure and to act as blow-back in the lter as hereinabove described or it may be by-passed through line 41 around the lter. This by-passing of the gas is necessary when the volume of blow-back gas is insuflicient to furnish the necessary refrigeration in cold propane storage tank 45 or when the blow-back gas is insufficient to maintain the desired ethane content of the diluent in said storage tank 45.

The dewaxed lubricating oil from surge tank 32, which may contain the first portion of wash oil introduced by pipe 48, is passed by pump 49 through line I6 into the jackets of exchangers i4 as hereinabove described. If scraped surface exchangers are used, I may jacket the operating mechanism by a seal l5a so that propane from around the shafts will not escape from the system. Pumpr 49 maintains a high enough pressure in this line to insure a good heat exchange,in other words, there is no substantial vaporization of propane in the exchangers. This mixture is passed through valve 56 to high pressure still 5l which is provided with suitable steam coil 52 and which is maintained at a pressure of about 200 pounds. Diluent is removed through pipe 53, condensed in coils 54 and passed through pipe 55 to high pressure propane storage tank 55. The oil which is practically denuded of diluent is passed through line 51 to intermediate pressure still 58. This still is provided with steam coil 59 which drives out the remaining small amount of diluent through pipe 60 to intermediate pressure gas storage tank 24, the pressure in still 56 being substantially the same as that in storage gas tank 24. The oil leaving still 55 through line 6I may be further treated and stripped with an inert gas to remove the last traces of propane. It may be taken to suitable storage tanks or to apparatus for acid treating, solvent extracting, claying, etc.

Melted wax from surge tank 35 is forced by pump 62 through pipe 63 into high pressure still 64 wherein the diluent is boiled out by steam coil 65, the pressure in this still being about 200 pounds. Diluent vvapors are passed through pipe 56 to condenser 54, pipe 55 and high pressure diluent storage tank 56.

Wax from the base of still 64 is passed through pipe 61 to still 58 which is provided with steam coil 69 and is at substantially the same pressure as intermediate pressure gas storage tank 24, so.

that diluent may be passed directly to this gas storage tank through line 16. Wax may be removed from the base of -still 68 through line 'H for further stripping or treatment.

Diluent from storagetank 35 may be vented through line 12 to gas tank 24. It will be seen that gas tank 24 serves many diverse and important functions. It acts as a reservoir for blow-back gas for the lter system. It acts as a surge tank for gases vented from the cold propane storage tank and the cold wax slurry tank as well as from the low pressure diluent removal stills and the wax surge tank. Since all of this apparatus is connected to a single surge tank the pressure throughout the system is equalized, which is an important feature from the safety standpoint. When a mixture of ethane and propane is used as a diluent this storage tank isV of still greater importance because it acts as a reservoir for the ethane fraction and by Varying the load on compressor 4I and the amount of diluent introduced from the high pressure diluent storage tank I may control the relative amounts of propane and ethane in various parts of the system.

Propane from storage tank 56 may be passed through pipe 13 and valve 'i4 into cold propane storage tank 45 wherein it is chilled by vaporization and by the vaporization of compressed gases introduced through pipe 42. Likewise, vapors from high pressure storage tank 56 may be passed by pipe "i5 in amounts controlled by valve 76 into gas storage tank 24.

Cold propane may be pumped from storage tank 45 by means of pump 'Il through pipe 'i8 to pipes 20, 2 and 36 respectively.

As hereinabove stated, my apparatus may be employed with a diluent having a substantially fixed boiling point, but I prefer to employ a dilu l ent which consists of a mixture of normally gaseous diluents having diiferent boiling points such as a mixture of propane and ethane. When such a mixture is used, the high pressure storage tank will contain chiefly propane, the intermediate pressure gas storage tank will contain chiey ethane and the relative amounts of propane and ethane in the low pressure diluent storage tank can be regulated by varying the amount of propane introduced. The use of this mixture of high and low boiling diluents is particularly valuable in maintaining the desired pressure differential in the continuous lter because if the diluent consists of a single hydrocarbon such as propane and the pressure is maintained by using propane gas there isa tendency for the gas to condense on the surface of the wax cake, to warm up and redissolve wax, and to carry this dissolved wax into the filtrate and into the pores of the filter. The use of ethane offers the further advantage of providing a more rapid temperature control; by increasing the amount of ethane which is liq ueed and then vaporized in cold propane storage tank 45 I may cool this cold diluent very rapidly and to very low temperatures. Also, the use of ethane makes it possible to operate the intermediate stage at a pressure high enough to obtain ltration and it may thereby eliminate the necessity of compressor 22 and decrease the cost of operating compressor 4 I While I have 'described in detail a preferred embodiment of my invention, it should be understood that I do not limit myself to any of the details hereinabove set forth. I contemplate the use of compressors, pumps, valves, gas and liquid Gil expedients may be necessary and I contemplate the jacketing of any portions of the apparatus wherein propane leaks might occur,` for instance, the jacketing of the the scrapers for the chillers. Likewise, I contemplate the use of insulation and the expeditious use of heat exchangers in accordance with sound engineering practice.

I claim: Y

The process of dewaxing employing a diluent and a condensible gas ina continuous filter system, which process comprises dissolving a Waxbearing oil in the diluent, cooling the solution to obtain a filterable Wax slurry, adding cold liqueed gas to said slurry, introducing the slurry and liquefied gas into the continuous filter, intropoWer means for operating.'

2,097,728 lines, pressure relief Valves, etc. Whenever these ducing condensible gas as such into said filter for maintaining the pressure differential therein, removing gas with ltrate and subsequently separating gas therefrom, compressing' and cooling the separated gas, ashing the cooled separated gas to partially liquefy it and cool it for addition to said slurry, introducing the ashed gas into a large storage reservoir, introducing gas from said reservoir to said gas-compressing and cooling means, and to said lter for maintaining pressure differential, removing diluent and additional condensible gas from said filtrate, returning said gas to said storage reservoir and returning saidrecovered diluent for admixture with further amounts of incoming waxy oil.

PERCY C. KEITH, JR. 

